rich repository of fats, proteins, carbohydrates, minerals, vitamins, and water that together with the albumen nourish a growing embryo; lipids and proteins for a yolk are formed in the liver and deposited in increasing quantity in an ovarian follicle over several weeks time; yolk granules become part of the cytoplasm (materials surrounding the nucleus) of the female germ cell (oocyte, the nucleus of the cell); yolk is surrounded by 2 thin membranes while in the ovary (oolemma and perivitelline membrane); when yolk accumulates enough nutrients to feed a developing embryo, the egg is ovulated into the oviduct; 2 more membranes are laid down in the infundibulum of the oviduct (middle continuous layer and extravitelline membrane); as the embryo grows the yolk is consumed and shrinks; absorbed into the embryo’s abdomen by the time of hatching